LEDs are increasingly in demand for many purposes because such devices efficiently produce high-intensity, high-quality light. Mobile phones, personal digital assistants, digital cameras, MP3 players, and other portable devices use SSL devices, such as white light LEDs, for background illumination. LEDs can be used for many other applications, such as ceiling panels, desk lamps, refrigerator lights, table lamps, street lights, and automobile headlights.
White light is desirable for many applications, but commonly available LEDs typically cannot directly produce white light. One conventional technique for emulating white light with LEDs includes depositing a converter material, such as a phosphor, on a light emitting material. For example, as shown in FIG. 1A, a conventional LED device 10 includes a support 2 carrying an LED die 4 and a converter material 6 deposited on the LED die 4. The LED die 4 can include one or more light emitting components. For example, as shown in FIG. 1B, the LED die 4 can include a silicon substrate 12, an N-type gallium nitride (GaN) material 14, an indium gallium nitride (InGaN) material 16 (and/or GaN multiple quantum wells), and a P-type GaN material 18 arranged in serial layers. The LED die 4 can also include a first contact 20 on the P-type GaN material 18 and a second contact 22 on the N-type GaN material 14. Referring to both FIGS. 1A and 1B, in operation, the InGaN material 16 of the LED die 4 emits a blue light that stimulates the converter material 6 to emit a light (e.g., a yellow light) at a desired frequency. The combination of the blue and yellow emissions appears white to human eyes if matched appropriately.
Another conventional construction of an SSL device 21 is shown in FIG. 2A. The device 21 has a generally flat surface 22 upon which LEDs 24 are mounted. The device 21 also includes a lens 28 formed over the LEDs 24. The lens 28 can include a converter material 26 within or upon the lens 28. This configuration produces light focused primarily in one direction: normal to the LEDs 24. FIG. 2B illustrates the angular distribution produced by a conventional LED device 21 shown in FIG. 2A. The illuminance level (indicated by line 31) produced by the device 21 is strongest at 0° (directly above the LEDs 24), and drops off to zero at the 90° station and the −90° station (to the left and right of the LEDs 24). This distribution is referred to as a circular distribution and is suitable for some lighting applications. However, many other applications can benefit from a more dispersed distribution of light. Accordingly, there remains a need for LED systems that produce other light distribution patterns.